This project is designed to determine the role of the cerebral cortex in the sensory function of the primate hand. Neurophysiological and psychophysical techniques will be used to examine how the somatosensory system integrates spatial information on the skin. A new computer controlled tactile stimulator which delivers spatially complex stimuli to a dense array of 144 miniature probes, developed during the previous project period, will be used to measure single unit responses in both primary and secondary somatosensory areas of the cerebral cortex of awake monkeys. These animals are trained in psychophysical experiments to respond to specific features of the stimulus, such as spatial frequency or direction of motion, permitting properties of single unit discharges to be correlated with the sensations produced by the stimulus in both monkeys and humans. The experiments described in this proposal address four major topics: (A) the coding of motion and its direction across the skin, (B) the coding of spatial frequency of textured surfaces, (C) the spatial organization of receptive fields of cortical neurons receiving inputs from different classes of cutaneous mechanoreceptors, and (D) functional comparison of activity in SI and SII cortices. These studies will provide the first neurophysiological studies of responses evoked by the OPTACON tactile display normally used as a sensory substitution aid for the blind and deaf. We will obtain important neurophysiological data on the tactile information processing capabilities of the cerebral cortex, the functional organization of three different cytoarchitectural areas, and the integration of information between the two hemispheres. The findings may have important clinical applications such as the development of more quantitative tests of sensory function in patients with neurological disorders or peripheral nerve injuries, and the improvement of sensory substitution aids for visually and/or hearing impaired individuals.